Biosynthesis of Anthraquinone by Cells ofGalium mollugoL. Grown in a Chemostat with Limiting Sucrose or Phosphate

Abstract

Growth and anthraquinone biosynthesis by Galium cells were examined in steady-state substrate limited conditions using a chemostat continuous culture technique. Steady-state growth was obtained in both sucroseand phosphate-limiting conditions for periods up to 60 d. In sucrose-limiting conditions three growth rates were investigated with doubling times (td) of 25 h, 35 h and 40 h, and phosphate-limited growth was obtained at id = 35 h. The kinetics of the growth response to a change in limiting substrate concentration in sucrose-limiting conditions was examined and found to follow closely that predicted by the application of Monod's (1950) model obtained for micro-organisms. The anthraquinone content of cells grown in phosphate and sucrose limitation was uniformly similar and at a relatively low level (0-68 mg g~1 dry wt.). When the substrate limitation was relieved by the addition of the limiting substrate, either phosphate, or sucrose, anthraquinone synthesis was markedly stimulated. The addition of the anthraquinone precursor, orthosuccinyl benzoic acid (OSB) greatly enhanced anthraquinone synthesis in phosphate-limiting conditions but not in sucrose-limited cells. The results show that growth limitation by phosphate and by sucrose causes a suppression of the rate of synthesis of the secondary metabolite anthraquinone in Galium cells and suggests that the metabolic point of suppression is different in each case.